Bicycle rear suspension system with controlled variable shock rate

ABSTRACT

A bicycle comprises a bicycle frame and a rear wheel suspension system that is attached to the frame. The rear wheel suspension system comprises a rear wheel swingarm and a shock absorber that is coupled to the swingarm. A change in vertical wheel travel (ΔVWT) of the rear wheel is related to a change in the length of the shock absorber (ΔSL), providing a shock rate (SR). The shock rate (SR) changes throughout the vertical wheel travel of the rear wheel, such that the change in the shock rate dSR/dVWT has a change in sign as the rear wheel travels through its vertical wheel travel. In each case, the rate of change of the shock includes a change in sign, from positive to negative or from negative to positive. In some embodiments, the swingarm may be attached to the frame at a single pivot point or through a linkage system.

RELATED APPLICATION

This patent application is a divisional of the U.S. patent applicationSer. No. 12/652,642, filed Jan. 5, 2010, and entitled “BICYCLE REARSUSPENSION SYSTEM WITH CONTROLLED VARIABLE SHOCK RATE, which is herebyincorporated by reference in its entirety and is a continuation-in-partof the U.S. patent application Ser. No. 12/505,830, filed Jul. 20, 2009,and entitled “BICYCLE REAR SUSPENSION SYSTEM WITH CONTROLLED VARIABLESHOCK RATE,” now issued as U.S. Pat. No. 7,784,810, which is herebyincorporated by reference in its entirety, which is a continuation ofthe U.S. patent application Ser. No. 11/274,395, filed Nov. 14, 2005,and entitled, “BICYCLE REAR SUSPENSION SYSTEM WITH CONTROLLED VARIABLESHOCK RATE,” now issued as U.S. Pat. No. 7,581,743, which is herebyincorporated by reference in its entirety.

FIELD OF THE INVENTION

The invention generally relates to a shock absorbing rear wheelsuspension apparatus for a bicycle, and more particularly to a rearwheel suspension having a controlled variable shock rate.

DESCRIPTION OF THE PRIOR ART

A variety of rear wheel suspension systems have been used on bicycles toimprove performance. Many of these suspension systems are complicatedstructures involving a plurality of frame members, linkages of theswingarm frame members to other bicycle frame members and theinstallation of a shock absorber within the frame members to control themotion of the swingarm and the rear wheel engaged therewith.

One such prior art suspension system is disclosed in U.S. Pat. No.6,361,059 which describes a bicycle with a rear wheel suspension havinga single pivot axis that is located proximate the bottom bracket of thebicycle frame. A top portion of the swingarm, proximate the seat stays,is engaged to a shock absorber which controls the motion of the rearwheel swingarm. Another prior art suspension system is disclosed in U.S.Pat. No. 6,206,397 in which a bottom portion of the swingarm is engagedby a first linkage proximate the bottom bracket, and an upper portion ofthe swingarm proximate the seat stay is engaged with a second linkageproximate the top tube of the bicycle frame. A shock absorber is engagedto the swingarm to control the motion of the swingarm and therefore therear wheel of the bicycle.

In analyzing the performance of bicycle frames including those disclosedin the prior art, a comparison can be made between the vertical wheeltravel distance that the rear wheel moves upward (ΔVWT) and the changein the length of the shock absorber (ΔSL). The ratio of these twomeasurements, the change in the shock absorber length divided by thechange in vertical rear wheel travel (ΔSL/ΔVWT) is called the shock rate(SR). In various bicycle frame designs, the shock rate can beapproximately constant, it can increase as the vertical wheel travelincreases or it can decrease as the vertical wheel travel increases.

Controlling the shock rate can provide improved bicycle performance andthe present invention is directed to a bicycle rear wheel suspensionsystem in which the shock rate is variable and controllable to provideimproved bicycle performance characteristics.

SUMMARY OF THE INVENTION

A bicycle comprises a bicycle frame and a rear wheel suspension systemthat is attached to the frame. The rear wheel suspension systemcomprises a rear wheel swingarm and a shock absorber that is coupled tothe swingarm to control the motion of a rear wheel of the bicycle. Achange in the vertical wheel travel (ΔVWT) of the rear wheel is relatedto a change in the length of the shock absorber (ΔSL), providing a shockrate (SR) according to the relationship: SR=ΔSL/ΔVWT.

The shock rate (SR) changes throughout the vertical wheel travel of therear wheel, such that the change in the shock rate dSR/dVWT has a changein sign as the rear wheel travels through its vertical wheel travel. Theshock rate may at first decrease in value and subsequently increase, orinitially increase in value and subsequently decrease throughout thevertical wheel travel of the rear wheel. In each case, the rate ofchange of the shock includes a change in sign, from positive to negativeor from negative to positive. In some embodiments, the swingarm may beattached to the frame at a single pivot point or through a linkagesystem.

In one aspect, a bicycle comprises a bicycle frame and a rear wheelsuspension system attached to the frame. In some embodiments, the rearwheel suspension system comprises a rear wheel swingarm comprising achain stay, a seat stay, and a front stay. The swingarm is attached tothe frame at a single pivot axis. The rear wheel swingarm furthercomprises a substantially horizontal link, a vertical link and a shockabsorber. The shock absorber is pivotally coupled at a first end to thevertical link and pivotally coupled at a second end to a top tube of thebicycle frame. The engagement of the shock absorber controls a motion ofa rear wheel (VWT) of the bicycle. In some embodiments, the horizontallink is pivotally coupled to the swingarm and the vertical link. In someof these embodiments, the vertical link is further couple to the mainframe of the bicycle. In further embodiments, the seat stay and thechain stay are attached together by the front stay.

Particularly, the shock absorber has a length (SL) between the first endand the second end, wherein a change in the vertical wheel travel (ΔVWT)of the rear wheel is related to a change in the length of the shockabsorber (ΔSL) to provide a shock rate (SR) according to therelationship:SR=ΔSL/ΔVWT

and wherein the shock rate (SR) changes throughout the vertical wheeltravel of the rear wheel, such that the change in the shock ratedSR/dVWT has a change in sign as the rear wheel travels through thevertical wheel travel. In some of these embodiments, the shock ratefirst decreases, then reaches a minimum value and then increasesthroughout the vertical wheel of the rear wheel.

In another aspect, a rear wheel suspension system for a bicyclecomprises a frame with a rear wheel swingarm attached to the frame at asingle pivot axis, wherein the swingarm comprises a chain stay, a seatstay, and a front stay. The rear wheel suspension system comprises asubstantially horizontal link, a vertical link, and a shock absorberpivotally coupled at a first end to the vertical link and directlypivotally coupled at a second end to a top tube of the bicycle frame,wherein the engagement of the shock absorber controls a motion of a rearwheel (VWT) of the bicycle. In some embodiments, the horizontal link ispivotally connected to the swingarm and the vertical link. In some ofthese embodiments, the vertical link is pivotally coupled to the mainframe of the bicycle. In further embodiments, the seat stay and thechain stay are attached together by the front stay.

Particularly, the shock absorber has a length (SL) between the first endand the second end, wherein a change in the vertical wheel travel (ΔVWT)of the rear wheel is related to a change in the length of the shockabsorber (ΔSL) to provide a shock rate (SR) according to therelationship:SR=ΔSL/VWT

and wherein the shock rate (SR) changes throughout the vertical wheeltravel of the rear wheel, such that the change in the shock ratedSR/dVWT has a change in sign as the rear wheel travels through thevertical wheel travel. In some of these embodiments, the shock ratefirst decreases, then reaches a minimum value and then increasesthroughout the vertical wheel of the rear wheel.

In another aspect, a rear wheel suspension system for a bicyclecomprises a frame with a rear wheel swingarm attached to the frame at asingle pivot axis, wherein the swingarm comprises a chain stay, a seatstay, and a front stay. The suspension system comprises a first link, asecond link, and a shock absorber that is engaged to control thevertical wheel travel (VWT) of a rear wheel of the bicycle. The shockabsorber has a first end, a second end and a length (SL) between thefirst end and the second end. The shock absorber is pivotally coupled atthe first end to the second link, and pivotally coupled to the bicycleframe at the second end and further, wherein the first link is pivotallyconnected to the swingarm and the second link,

wherein the first link, second link and the shock absorber areconfigured such that a change in vertical wheel travel (ΔVWT) of therear wheel is related to a change in the length of the shock absorber(ΔSL) to provide a shock rate (SR) according to the relationship:SR=ΔSL/VWT

and wherein the shock rate (SR) changes throughout the vertical wheeltravel of the rear wheel, such that the change in the shock ratedSR/dVWT has a change in sign as the rear wheel travels through thevertical wheel travel. In some embodiments, the shock rate firstdecreases, then reaches a minimum value and then increases throughoutthe vertical wheel travel of the rear wheel. In some of thesesembodiments, the sign change is from negative to positive. In someembodiments, the shock rate first increases, then reaches a maximumvalue and then decreases throughout the vertical wheel travel of therear wheel. In some of these embodiments, the sign change is from apositive to a negative.

In yet another aspect, a bicycle comprises a bicycle frame and a rearwheel suspension system attached to the frame. The rear wheel suspensionsystem comprises a rear wheel swingarm comprising a chain stay, a seatstay, and a front stay, wherein the seat stay and the chain stay areattached together by the front stay, and further wherein the swingarm isattached to the frame at a single pivot axis. The rear wheel suspensionsystem further comprises a substantially horizontal link, a verticallink, and a shock absorber pivotally coupled at a first end to thevertical link and pivotally coupled at a second end to the bicycleframe, wherein the engagement of the shock absorber controls a motion ofa rear wheel (VWT) of the bicycle, wherein the shock absorber has alength (SL) between the first end and the second end, wherein a changein the vertical wheel travel (ΔVWT) of the rear wheel is related to achange in the length of the shock absorber (ΔSL) to provide a shock rate(SR) according to the relationship:SR=ΔSL/VWT

and wherein the shock rate (SR) changes throughout the vertical wheeltravel of the rear wheel, such that the change in the shock ratedSR/dVWT has a change in sign as the rear wheel travels through thevertical wheel travel. In some embodiments, the shock absorber ispivotally coupled at the first end to the vertical link and pivotallycoupled at the second end to a top tube of the bicycle frame. In someembodiments, the shock absorber is pivotally coupled at the first end tothe vertical link and pivotally coupled at the second end to a down tubeof the bicycle frame.

IN THE DRAWINGS

FIG. 1 is a schematic drawing of a side view of a bicycle illustratingan embodiment of a wheel suspension system of the present invention;

FIG. 2 is an enlarged drawing of the bicycle depicted in FIG. 1;

FIG. 3 is a graph depicting the shock rate versus vertical wheel travelof the bicycle depicted in FIGS. 1 and 2;

FIG. 4 is a graph depicting the change in the shock rate versus verticalwheel travel of the bicycle depicted in FIGS. 1 and 2;

FIG. 5 is a side elevational view of a bicycle frame corresponding tothe schematic drawings of FIGS. 1 and 2;

FIG. 6 is a perspective view of the bicycle frame depicted in FIG. 5;

FIG. 7 is a side view of a bicycle illustrating another embodiment of awheel suspension system of the present invention;

FIG. 8 is a graph depicting the shock rate versus vertical wheel travelof the bicycle depicted in FIG. 7;

FIG. 9 is a graph depicting the change in the shock rate versus verticalwheel travel of the bicycle depicted in FIG. 7;

FIG. 10 is a schematic view of a bicycle illustrating another embodimentof a wheel suspension system of the present invention;

FIG. 11 is an enlarged drawing of the bicycle depicted in FIG. 10;

FIG. 12 is a graph depicting the shock rate versus vertical wheel travelof the bicycle depicted in FIG. 7;

FIG. 13 is a graph depicting the change in the shock rate versusvertical wheel travel of the bicycle depicted in FIG. 7;

FIG. 14 is a side view of a bicycle illustrating another embodiment of awheel suspension system of the present invention;

FIG. 15 is a graph depicting the shock rate versus vertical wheel travelof the bicycle depicted in FIG. 7;

FIG. 16 is a graph depicting the change in the shock rate versusvertical wheel travel of the bicycle depicted in FIG. 7;

FIG. 17 illustrates a side elevational view of a bicycle frame inaccordance with some embodiments;

FIG. 18 illustrates a perspective view of the bicycle frame depicted inFIG. 17 in accordance with some embodiments; and

FIG. 19 illustrates a side elevational view of a bicycle frame inaccordance with some embodiments.

DETAILED DESCRIPTION

FIG. 1 depicts a first embodiment of a rear wheel suspension system 10engaged with a bicycle frame 12 of a bicycle 13 of the presentinvention. The bicycle frame 12 generally includes a seat tube 14 and adown tube 18, both of which are attached to a bottom bracket 22 thathouses a pedal assembly 26, a top tube 30, and a front fork 34. Theseselements are typically welded or otherwise secured together to definethe frame 12 of the bicycle. Although the frame 12 typically includesall of the foregoing members, alternate embodiments can have more orless than all of the foregoing members, and can include them in variousforms, sizes, and configurations, and still achieve the intendedfunctionality and beneficial aspects of the invention.

The rear wheel suspension system 10 generally includes a rear wheelswingarm 40 that includes a pair of seat stays 44 and a pair of chainstays 48 that are joined to each other at their rearward ends 52proximate the axle 56 of the rear wheel 60. A pair of front stays 64 areengaged between the chain stays 48 and the seat stays 44 to provide arigid triangular structure for the swingarm. A shock absorber 80 isengaged to the swingarm to control the motion of the swingarm relativeto the bicycle frame members, thereby controlling the motion of the rearwheel. In a typical configuration of the swingarm 40, the seat stays 44,chain stays 48 and front stays 64 are provided in corresponding pairs,with one stay member of each pair positioned on either side of the rearwheel. The rear wheel suspension stays 44, 48 and/or 64 can also includeone or more elements such as conventional braze-on elements (not shown)to secure cables and brakes and the like to the frame and keep them awayfrom interfering with the movement and operation of the bicycle. Personsof ordinary skill in the art will appreciate that the exactconfiguration and relationship between the seat stays, chain stays,front stays and attachment points with frame members can vary dependingon, among other things, the size of the bicycle frame, and the size ofthe rear wheel.

In the bicycle embodiment 13 depicted in FIG. 1, the lower frontward endof the swingarm structure 40, proximate the frontward end 88 of thechain stays 48, is pivotally attached utilizing a pivot pin 94 or thelike to the bicycle frame 12 proximate the bottom bracket 22, such thatthe swingarm rotates about the single pivot axis 94. The upper end ofthe swingarm, proximate the frontward end 98 of the seat stays 44 isengaged through a linkage structure 102 to the bicycle frame proximatethe joinder of the seat tube 14 and top tube 30. The shock absorber 80is engaged with the linkage to control the motion of the swingarm. Adetailed description of the shock absorber engagement with the swingarmlinkages and the controlled motion of the swingarm is also providedherebelow with the aid of FIG. 2.

When the bicycle depicted in FIG. 1 is utilized, the rear wheel isdesigned to move generally vertically upward 104 about the single pivotaxis 94 when the rear wheel encounters an obstacle such as roughterrain. Such a vertical wheel movement creates a corresponding changein the length of the shock absorber as the shock absorber piston armmoves inwardly or outwardly in response to the rear wheel verticalmotion. A significant performance characteristic of the bicycle frame isrelated to the relationship between the change in shock absorber length(ΔSL) and the change of the vertical wheel travel (ΔVWT) relatedthereto. This parameter is called the “shock rate” (SR) where:SR=ΔSL/ΔVWTAs described herebelow, with an appropriate swingarm and linkageconfiguration the shock rate can be advantageously controlled, andspecifically, the present invention relates to the swingarm and linkageconfigurations in which the shock rate is controlled such that itinitially increases and then decreases throughout the vertical wheeltravel, or it initially decreases and subsequently increases throughoutthe vertical wheel travel. The rate of change of the shock rate withrespect to the vertical wheel travel dSR/dVWT therefore undergoes a signchange, either from positive to negative or negative to positive, as therear wheel travels vertically. Detailed descriptions of exemplaryembodiments of the present invention are next presented.

FIG. 2 is an enlarged depiction of the invention shown in FIG. 1comprising a suspension system that moves the rear wheel axle 56 via aswingarm 40 about a single pivot 94. The swingarm motion is resisted bythe shock-absorber 80, where the rate of vertical motion of the rearaxle changes with respect to the rate of compression of the shockabsorber according to the relationship SR=ΔSL/ΔVWT as is describedabove.

The shock-absorber compression is controlled at one end by a pluralityof links of the linkage 102, driven by the swingarm motion. This linkage102 includes a straight connecting link 120 and a rocker link 124. Theconnecting link 120 is pivotally attached by a pivot 126 at a first end128 to the forward end 98 of the seat stay 44, and pivotally attached ata second end 132 to a first arm 136 of the rocker link 124.

The rocker link 124 is pivotally attached at a generally centrallylocated pivot point 144 to the bicycle frame 12 and rotates about thispivot 144. A second arm of the rocker link 124 is pivotally attached tothe upper end 156 of the piston arm of the shock absorber 80. The lowerend 160 of the shock absorber 80 is pivotally attached to the frontstays 64 of the swingarm 40 with a shock mount 168, although it can alsobe attached to the chain stay 48.

If a first exemplary embodiment of the present invention 13, theswingarm includes a chain stay having a length of approximately 450 mmand a seat stay having a length of approximately 400 mm, where theincluded angle c between the chain stay and seat stay is approximately20 degrees. The shock absorber is a compression shock absorber having anuncompressed length of approximately 200 mm, with a usable stroke ofapproximately 50 mm, such as a shock absorber manufactured by Fox RacingShox, model Float R. The connecting link has a pivot to pivot length ofapproximately 60 mm, the first arm of the rocker link has a pivot topivot length of approximately 50 mm and the second arm of the rockerlink has a pivot to pivot length of approximately 45 mm, where theincluded angle between the arms of the rocker link is approximately 130degrees. The lower shock mount position 168 is approximately 57 mmabove, and 83 mm behind the swingarm pivot axis 94.

The swingarm pivot axis 94 is located approximately 70 mm above the axis108 of the drive sprocket 110 of the bottom bracket 22. The horizontaldistance between the swingarm pivot axis 94 and the drive sprocket axis108 can be altered to suit various frame configurations. The anglebetween rocker link arm 152 and the shock absorber is generally acute atthe beginning of travel (approximately 20 degrees), and becomes lessacute as the suspension is compressed, with a total angle change ofapproximately 45 degrees throughout the range of travel.

The stationary pivot 144 of the rocker link 124 is located above andrearward of the main swingarm pivot 94, and above and forward of theconnecting link/seat stay pivot 126. The connecting link/seat stayattachment point 126 is located above and rearward of the swingarm pivotaxis 94, and the placement of the swingarm shock mount 168 is above andrearward of the swingarm pivot 94.

During rear wheel vertical travel, the rocker link 124 rotates in acounter-clockwise direction, with an increasing angular velocity duringthe first part of the wheel travel to a maximum angular velocityapproximately halfway through the travel, and a decreasing angularvelocity throughout the second portion of the wheel travel. Theconnecting link 120 rotates in a clockwise direction, and the angularvelocity of the connecting link decreases during the range of verticalwheel travel. Where a different shock absorber is utilized, having adiffering length or where a different amount of vertical wheel travel isdesired, the dimensions given above may be varied in such a manner as toachieve the desired variable shock rate properties of the presentinvention.

It can therefore be appreciated that as the swingarm moves upward, theshock absorber compression is changed by both the motion of the links asdescribed, and the motion of the swingarm. The sum of the rocker linkmotion and swingarm shock mount motion is configured to change the shockcompression rate (SR) as the swingarm is moved throughout the range oftravel, and FIG. 3 is a graph that depicts the shock rate (SR)throughout the vertical wheel travel (VWT) of the swingarm 40.

As can be seen in FIG. 3, the shock rate (SR) has an initial portion 172that decreases in value, has a portion 176 of essentially zero change invalue and a portion 180 of increasing value. FIG. 4 is a graph depictingthis change in the shock rate with respect to the vertical wheel travel.The rate of change in the shock rate is seen to first be negative 184,then zero 188, and then positive 192 throughout the vertical wheeltravel. The result is a shock rate that has a rate of change (dSR/dVWT)that has a negative value during the first portion 184 of the wheeltravel, goes through a sign change at a zero change rate 188, andchanges to a positive value during the later portion 192 of the wheeltravel as shown in FIGS. 3 and 4.

For ease of comprehension, an exemplary bicycle frame is depicted inFIGS. 5 and 6 to illustrate how a bicycle frame can be constructed usingthe schematic shown of the linkage in FIGS. 1 and 2. FIG. 5 is a sideelevational view and FIG. 6 is a perspective view taken from a rearwardviewpoint towards the front of the bicycle frame, and structuralelements of the frame depicted in FIGS. 5 and 6 that correspond tostructural elements previously described with regards to FIGS. 1 and 2are correspondingly numbered for ease of comprehension.

As depicted in FIGS. 5 and 6, the bicycle frame 12 generally includesthe seat tube 14 and down tube 18, both of which are attached to abottom bracket 22 that houses a pedal assembly 26, and the top tube 30.The rear wheel suspension system 10 generally includes the rear wheelswingarm 40 that includes the pair of seat stays 44 and chain stays 48that are joined to each other at their rearward ends 52 proximate therear wheel axle 56. The front stays 64 are engaged between the chainstays 48 and the seat stays 44 and the shock absorber 80 is engaged tothe swingarm to control the motion of the swingarm relative to thebicycle frame members, thereby controlling the motion of the rear wheel.

The lower frontward end of the swingarm structure 40, proximate thefrontward end of the front stays 64, is pivotally attached utilizing apivot pin 94 or the like to the bicycle frame proximate the bottombracket 22, such that the swingarm rotates about the single pivot axis94. The upper end of the swingarm, proximate the frontward end 98 of theseat stays 44 is engaged through the linkage structure 102 to thebicycle frame proximate the joinder of the seat tube 14 and top tube 30.

The linkage 102 includes the connecting link 120 and the rocker link124. The connecting link is pivotally attached by a pivot 126 at a firstend 128 to the forward end 98 of the seat stay 44, and pivotallyattached at a second end 132 to a first arm 136 of the rocker link 124.The rocker link 124 is pivotally attached at a pivot point 144 to thebicycle frame 12, and rotates about this pivot 144, and the second arm152 of the rocker link 124 is pivotally attached to one end 156 of theshock-absorber 80. The second end 160 of the shock-absorber 80 ispivotally attached to the front stays 64 of the swingarm 40.

Various linkage configurations can be employed by those versed in theart to achieve a sign change of the dSR/dVWT value for varying amountsof rear wheel travel, as well as the peak values of both negative andpositive values among others. The linkage shown is merely one embodimentof a bicycle suspension which has a rear axle path based on a singlepivot.

Another example of a single pivot point bicycle frame 200 of the presentinvention is depicted in FIG. 7, and structural elements of the framedepicted in FIG. 7 that correspond to structural elements previouslydescribed with regard to FIGS. 1, 2, 5 and 6 are correspondinglynumbered for ease of comprehension. As is discussed below, in frame 200the swingarm motion is resisted by the shock-absorber, where the rate ofvertical motion of the rear axle changes with respect to the rate ofcompression of the shock absorber according to the relationshipSR=ΔSL/ΔVWT, wherein dSR/dVWT has a sign change, as is described above.

As depicted in FIG. 7, the bicycle frame 200 generally includes the seattube 14 and down tube 18, both of which are attached to a bottom bracket22, and the top tube 30. The rear wheel suspension system 210 generallyincludes the rear wheel swingarm 240 that includes the pair of seatstays 244 and chain stays 248 that are joined to each other at theirrearward ends 252 proximate the rear wheel axle 256. The front stays 264are engaged between the chain stays 248 and the seat stays 244 and theshock absorber 280 is engaged to the swingarm to control the motion ofthe swingarm relative to the bicycle frame members, thereby controllingthe motion of the rear wheel.

The lower frontward end of the swingarm structure 240, proximate thefrontward end of the front stays 263, is pivotally attached utilizing apivot pin 294 or the like to the bicycle frame proximate the bottombracket 22, such that the swingarm rotates about the single pivot axis294. The upper end of the swingarm, proximate the frontward end 298 ofthe seat stays 244 is engaged through the linkage structure 302 to thebicycle frame proximate the joinder of the seat tube 14 and the top tube30. The shock-absorber compression is controlled at one end by aplurality of links of linkage 302, driven by the swingarm motion. Thislinkage 302 includes a straight connecting link 320 and a rocker link324. The connecting link 320 is pivotally attached by a pivot 326 at afirst end 328 to the forward end 298 of the seat stay 244, and pivotallyattached at a second end 332 to a first arm 336 of the rocker link 324.

The rocker link 324 is pivotally attached at a generally centrallylocated pivot point 344 to the bicycle frame 12 and rotates about thispivot 344. A second arm 352 of the rocker link 324 is pivotally attachedto one end 356 of the piston arm of the shock-absorber 280. The secondend 360 of the shock-absorber is pivotally attached proximate the frontstays 264 of the swingarm 240 with a shock mount 368, although it canalso be attached to the chain stays 248.

In a second exemplary embodiment of the invention 200, the swingarmincludes a chain stay having a length of approximately 500 mm and a seatstay having a length of approximately 450 mm, where the angle betweenthe chain stay and the seat stay is approximately 18 degrees. The shockabsorber is a compression shock absorber having an uncompressed lengthof approximately 200 mm, with a usable stroke of approximately 50 mm,such as a shock absorber manufactured by Fox Racing Shox, model Float R.The connecting link has a pivot to pivot length of approximately 55 mm,the first arm of the rocker link has a pivot to pivot length 36 mm andthe second arm of the rocker link has pivot to pivot length ofapproximately 50 mm, where the angle between the arms of the rocker linkis approximately 158 degrees.

The swingarm pivot axis 294 is located approximately 70 mm above theaxis of the bottom bracket 22. The horizontal distance between theswingarm pivot axis 294 and the bottom bracket axis 22 can be altered tosuit various frame configurations. The angle between the rocker link arm352 and the shock absorber is generally acute at the beginning of thetravel (approximately 43 degrees), and becomes less acute as thesuspension is compressed, with a total angle change of approximately 40degrees throughout the range of travel. The position of the lower shockmount 368 on the swingarm is 35 mm behind and 55 mm above the swingarmpivot axis 294.

The stationary pivot 344 of the rocker link 124 is located above andslightly forward of the main swingarm pivot 294, and above and forwardof the connecting link/seat stay pivot 326. The connecting link/seatstay attachment point 326 is located above and rearward of the swingarmpivot axis 294, and the placement of the swingarm shock mount 368 isabove and rearward of the swingarm pivot 294.

During rear wheel upward travel, the rocker link 324 rotates in acounter-clockwise direction, with an increasing angular velocity. Theconnecting link 320 rotates in a clockwise direction, and the angularvelocity of the connecting link increases during the range of verticalwheel travel. Where a different shock absorber is utilized, having adiffering length or where a different amount of vertical wheel travel isdesired, the dimensions given above may be varied in such a manner as toachieve the desired variable shock rate properties of the presentinvention.

It can therefore be appreciated that as the swingarm moves upward, theshock compression is changed by both the motion of the links asdescribed, and the motion of the swingarm. The sum of the rocker linkmotion and swingarm shock motion is configured to change the shockcompression rate (SR) as the swingarm is moved throughout the range oftravel, and FIG. 8 is a graph that depicts the shock rate (SR)throughout the vertical wheel travel (VWT) of the swingarm 240.

As can be seen in FIG. 8, the shock rate (SR) has as initial portion 372that increases in value, has a portion 376 of essentially zero change invalue and a portion 380 of decreasing value. FIG. 9 is a graph depictingthis change in the shock rate with respect to the vertical wheel travel.The rate to change in the shock rate is seen to first be positive 384,then zero 388, and then negative and decreasing 392 throughout thevertical wheel travel. The result is a shock rate that has a rate ofchange (dSR/dVWT) that has a positive value during the first portion 384of the wheel travel, goes through a sign change at a zero change rate388, and changes to a negative value during the later portion 392 of thewheel travel as shown in FIGS. 8 and 9.

Various linkage configurations can be employed by those versed in theart to achieve sign change of the dSR/dVWT value for varying shockabsorbers and varying amounts of rear wheel travel, as well as the peakvalues of both negative and positive values among others. The linkagesshown are merely exemplary embodiments of a bicycle suspension which hasa rear axle path based on a single pivot.

FIG. 10 is a schematic diagram showing another bicycle embodiment 400 ofthe present invention using a suspension system 402 that moves the rearwheel axle 404 via a swingarm 408 connected to a pair of linkages 412and 416 that are each pivotally attached at one end to the swingarm 408,and pivotally attached at a second end to the mainframe 420 of thebicycle 400; FIG. 11 is an enlarged depiction of the bicycle 400depicted in FIG. 10. The frame 420 includes the seat tube 14, down tube18, and top tube 30, and the swingarm 408 includes seat stays 444, chainstays 448 and front stays 464. The swingarm motion is resisted by ashock absorber 424, such that the shock absorber rate SR varies withvertical wheel travel, and the rate of change of the shock rate dSR/dVWThas a change in sign during the vertical wheel travel, as has beendescribed above.

As is best seen in FIG. 11, the lower linkage 412 includes a connectinglink 430 that is pivotally attached at its rearward end 432 to the lowerforward corner 434 of the swingarm 408, and pivotally attached at itsforward end pivot attachment 442 to the main frame 420 proximate thebottom bracket 440. The link 430 is also pivotally connected proximateits rearward end 432 to the lower end 445 of the shock absorber 424.

The upper linkage 416 includes a rocker link 454 that includes a firstarm 456 that is pivotally attached at a pivot 457 to the upper forwardcorner 458 of the swingarm 408 at one end, and connected at a centralpivot 466 to the mainframe of the bicycle 400 proximate the middle ofthe rocker link 454. The shock absorber 424 is pivotally connected atits upper end 460 to the outer end of the second arm 468 of the rockerlink 454.

In an exemplary embodiment of the present invention 400, the swingarmincludes a chainstay 448 having a length of approximately 400 mm and aseat stay 444 having a length of approximately 490 mm, where theincluded angle between the chain stay and the seat stay is approximately26 degrees. A suitable shock absorber is a compression shock absorberhaving an uncompressed length of approximately 297 mm, with a usablestroke of approximately 60 mm. The connecting link 430 has a pivot topivot length of approximately 18 mm, the first arm 456 of the rockerlink 454 has a pivot to pivot length of approximately 65 mm and thesecond arm 468 of the rocker link has a pivot to pivot length ofapproximately 59 mm, where the included angle between the arms of therocker link is approximately 116 degrees. The angle between rocker linkarm 468 and the shock absorber is generally acute at the beginning ofthe travel (approximately 62 degrees), and becomes less acute as thesuspension is compressed, with a total angle change of approximately 25degrees throughout the range of travel.

The stationary pivot 466 of the rocker link 454 is located above andslightly forward of the pivot attachment 442 of the connecting link 430,and above and slightly rearward of the upper swingarm connecting pivot457. The rocker link 454 rotates in a counter-clockwise direction, withan increasing angular velocity during the first part of wheel travel toa maximum angular velocity approximately halfway through the travel, anda decreasing angular velocity throughout the second portion of the wheeltravel. The connecting link 430 rotates in a clockwise direction, andthe angular velocity of the connecting link increases during the rangeof vertical wheel travel. Where a different shock absorber is utilized,having a differing length or where a different amount of vertical wheeltravel is desired, the dimensions given above may be varied in such amanner as to achieve the desired variable shock rate properties of thepresent invention.

As the swingarm is moved during vertical wheel travel, the shock rate(SR) has a rate of change (dSR/dVWT) that has a positive value duringthe first portion of the wheel travel, and changes sign to a negativevalue during the later portion of the travel as shown in FIGS. 12 and 13due to the combined motion of the first and second linkages.

FIG. 12 is a graph that depicts the shock rate (SR) throughout thevertical wheel travel (VWT) of the swingarm 408. As can be seen in FIG.12, the shock rate (SR) has an initial portion 480 that increases invalue, has a portion 484 of essentially zero change in value, and aportion 488 of decreasing value. FIG. 13 is a graph depicting thischange in the shock rate with respect to the vertical wheel travel. Therate of change in the shock rate is seen to have an initial portion 490to first be positive, then a sign change 494 and then a portion 498 thatis negative in value throughout the vertical wheel travel.

FIG. 14 depicts another bicycle embodiment 500 of the present inventionusing a suspension system 502 that moves the rear wheel axle 504 via aswingarm 508 connected to a pair of linkages 512 and 516 that are eachpivotally attached at one end to the swingarm 508. and pivotallyattached a second end of the mainframe 520 of the bicycle 500. The frameincludes the seat tube 14, down tube 18, and top tube 30, and theswingarm 508 includes seat stays 544, chain stays 548 and front stays564. The swingarm motion is resisted by a shock absorber 524, such thatthe shock rate SR varies with vertical wheel travel, and the rate ofchange of the shock rate dSR/dVWT has a change in sign during thevertical wheel travel, as has been described above.

The lower linkage 512 includes a connecting link 530 that is pivotallyattached at its rearward end 532 to the lower forward corner 534 of theswingarm 508, and pivotally attached at its forward end 542 to the mainframe 520 proximate the bottom bracket 540. The link 530 is alsopivotally connected on its rear pivot axis 532 to the lower end of theshock absorber 524.

The upper linkage 516 includes a rocker link 554 that includes a firstarm 556 that is pivotally attached to the upper forward corner 558 ofthe swingarm 508 at one end, and connected at a central pivot 566 to themainframe of the bicycle proximate the middle of the rocker link 554.The shock absorber 524 is pivotally connected at its upper end 560 tothe outer end pivot 567 of the second arm 568 of the rocker link 554.

In an exemplary embodiment of the present invention 500, the swingarmincludes a chain stay 548 having a length of approximately 400 mm and aseat stay 544 having a length of approximately 480 mm, where theincluded angle between the chain stay and the seat stay is approximately27 degrees. A suitable shock absorber is a compression shock absorberhaving an uncompressed length of approximately 320 mm, with a usablestroke of approximately 50 mm. The connecting link 530 has a pivot topivot length of approximately 18 mm. The first arm 556 of the rockerlink 554 has a pivot to pivot length of approximately 60 mm, where theincluded angle between the arms of the rocker link is approximately 116degrees. The angle between the rocker link arm 568 and the shockabsorber is generally acute at the beginning of the travel(approximately 49 degrees), and becomes less acute as the suspension iscompressed, with a total angle change of approximately 35 degreesthroughout the range of travel.

The stationary pivot 566 of the rocker link 554 is located above andforward of the axis of the bottom bracket 540, and above and slightlyrearward of the upper swingarm link pivot 558. The rocker link 554rotates in a counter-clockwise direction, with an increasing angularvelocity during the first part of the wheel travel to a maximum angularvelocity approximately halfway through the travel, and a decreasingangular velocity throughout the second portion of the wheel travel. Theconnecting link 530 rotates in a clockwise direction, and the angularvelocity of the connecting link decreases during the range of verticalwheel travel. Where a different shock absorber is utilized, having adifferent length or where a different amount of vertical wheel travel isdesired, the dimensions given above may be varied in such a manner as toachieve the desired variable shock rate properties of the presentinvention.

As the swingarm is moved during vertical wheel travel, the shock rate(SR) has a rate of change (dSR/dVWT) that has a negative value duringthe first portion of the wheel travel, and changes sign to a positivevalue during the later portion off the travel as shown in FIGS. 15 and16 due to the combined motion of the first and second linkages.

FIG. 15 is a graph that depicts the shock rate (SR) throughout thevertical wheel travel (VWT) of the swingarm 508. As can be seen in FIG.15, the shock rate (SR) has an initial portion 580 that decreases invalue, has a portion 584 of essentially zero change in value, and aportion 488 of increasing value. FIG. 16 is a graph depicting thischange in the shock rate with respect to the vertical wheel travel. Therate of change in the shock rate is seen to have an initial portion 590to first be negative, then a sign change 594 and then a portion 598 thatis positive in value throughout the vertical wheel travel.

A feature of some of the exemplary embodiments of the present inventionis that neither of the two ends of the shock absorber is directlyengaged to the main frame of the bicycle, however this shock absorberengagement configuration is not required in order to realize thevariable shock rate feature of the a bicycle of the present invention.For instance, regarding the exemplary embodiment of a single pivotswingarm bicycle, depicted in FIGS. 1-9, the lower end of the shockabsorber is pivotally engaged to the swingarm, and the swingarm is thenpivotally engaged to the bicycle frame at a single pivot point 94. Theupper end of the shock absorber is engaged to the rocker link 124, whichis then engaged at its central pivot point to the main frame of thebicycle. With regard to the bicycles 400 and 500, both the lower end andthe upper end of the shock absorber are engaged to links that arepivotally attached to the main frame. Thus, in some of the exemplaryembodiments of the present invention, neither end of the shock absorberis directly engaged to the main frame of the bicycle, such as through asingle pivot point engagement.

A further example of a single pivot bicycle frame is shown in FIGS.17-19. FIGS. 17 and 19 illustrates a side elevational view of a bicycleframe in accordance with some embodiments and FIG. 18 illustrates aperspective view of the bicycle frame depicted in FIG. 17. Structuralelements corresponding to structural elements previously described withregard to FIGS. 1, 2, 5, and 6 are correspondingly numbered for ease ofcomprehension.

The bicycle frame 600 comprises a seat tube 14, a top tube 30, and adown tube 18. The down tube 18 and the seat tube 14 meet at a bottombracket 22. The bicycle frame 600 further comprises a rear wheelsuspension system 610 attached to the main frame 612. The rear wheelsuspension system 610 comprises a rear wheel swingarm 640, one or moreseat stays 644, one or more chainstays, one or more front stays 664 oruprights, a linkage system 620, and a shock absorber 680. The one ormore seat stays 644 and the one or more chan stays 648 are joinedtogether at a back end 652 proximate the rear wheel axle 656. The one ormore front stays or uprights 664 is engaged between the one or more seatstays 644 and the one or more chain stays 648. In some embodiments ofthe swingarm 640, the seat stays 644, chain stays 648 and front stays664 are provided in corresponding pairs, with one stay member of eachpair positioned on either side of the rear wheel. The shock absorber 680is pivotally coupled at a first end to the linkage system 620 andpivotally coupled at a second end to the main frame 612.

As shown in FIGS. 17-19, the swingarm 640 is attached to the mainportion of the bicycle frame 612 at a single pivot point 694 proximatethe bottom bracket 22. The lower frontward end of the swingarm 640 ispivotally coupled to the main frame 612 at the pivot point 694 utilizinga pivot pin or other appropriate mechanism as known in the art. In thisconfiguration, the swingarm 640 is able to rotate about the pivot axis694. The upper forward end of the swingarm 640 is pivotally coupled tothe main portion of the bicycle frame 612 through a linkage system 620at the pivot point 626. As described above, the shock absorber 680 ispivotally coupled to the linkage system 620 to control the motion of theswingarm 640.

As further shown in FIGS. 17-19, the linkage system 620 comprises asubstantially horizontal connecting link 628 (first link) and asubstantially vertical swing link 670 (second link). The connecting link628 is pivotally coupled by a pivot 626 at a first end to the upperforward end of the swingarm 640, and pivotally coupled at a second endto the swing link 670 by a pivot 660. The swing link 670 is pivotallycoupled to the main frame of the bicycle at an upward end of the swinglink 670 at a pivot point 676, and rotates about this pivot. In someembodiments, the swing link 670 is pivotally coupled to the seat tube 14of the main frame 612 at the pivot point. The swing link 670 ispivotally coupled to a first end of shock absorber 680 at the lower endof the swing link 690.

As described above, the shock absorber 680 is pivotally coupled at afirst end to the linkage system 620 and pivotally coupled at a secondend to the main frame 612. In some embodiments, the shock absorber 680is pivotally coupled at the first end to the swing link 670 at the lowerend of the swing link 690 and pivotally coupled at the second end to themain frame 612 at the pivot point 656. As shown in FIGS. 17 and 18, thesecond end of the shock absorber 680 is pivotally coupled to the toptube 30 of the main frame 612. However, in some embodiments, the secondend of the shock absorber 680 is able to be coupled to any portion orcomponent of the main frame 612.

FIG. 19 illustrates a single pivot bicycle frame in accordance with someembodiments. The shock absorber 680 is pivotally coupled at a first endto the linkage system 620 and pivotally coupled at a second end to themain frame 612. As shown in FIG. 19, the second end of the shockabsorber 680 is pivotally coupled to the down tube 18 of the main frame612.

When the bicycle and rear suspension illustrated in FIGS. 17, 18 and 19is utilized, the rear wheel is designed to move generally verticallyupward about the single pivot axis 694 when the rear wheel encounters anobstacle such as rough terrain. As described above, the motion of theswingarm 640 is resisted by the shock-absorber 680, where the rate ofvertical motion of the rear axle changes with respect to the rate ofcompression of the shock absorber 680. As further described above, therate of vertical motion of the rear axle changes with respect to therate of compression of the shock absorber 680 according to therelationship SR=ΔSL/ΔVWT, wherein dSR/dVWT has a sign change, as isdescribed above. In some embodiments, the shock rate first decreases,then reaches a minimum value and then increases throughout the verticalwheel travel of the rear wheel. In some embodiments, the shock ratefirst increases, then reaches a maximum value and then decreasesthroughout the vertical wheel travel of the rear wheel.

The upper pivot 676 of the swing link 670 is located above and forwardof the axis of the bottom bracket 22 and above and slightly forward ofthe lower pivot 660 of the swing link 670. During rear wheel upwardtravel, the swing link 670 rotates in a counter-clockwise direction andthe connecting link 628 rotates in a clockwise direction. Accordingly,as the swingarm 640 moves upward, shock absorber 680 compression ischanged by both the motion of the linkage system 620 as described, andthe motion of the swingarm 640.

As further described above, various linkage configurations are able tobe employed by those versed in the art to achieve a sign change of thedSR/dVWT value for varying amounts of rear wheel travel, as well as thepeak values of both negative and positive values among others. Thelinkage shown is merely one embodiment of a bicycle suspension systemwhich has a rear axle path based on a single pivot.

Generally, suspension systems are used for making a vehicle morecomfortable to ride, as well as increasing traction and vehicle controlby keeping the wheels on the ground. An advantage of using a bicyclehaving a changing shock rate that has a sign change from negative topositive is that it can increase rider comfort by providing morevertical wheel travel to prevent it from bottoming out, causingdiscomfort when a large impact is experienced.

Using a bicycle having a shock rate having a sign change from positiveto negative has advantages for certain applications. In this case, thefirst part of suspension travel gives the wheel a high mechanicaladvantage, allowing the wheel to stay on the ground at high speeds andthrough depressions without disrupting the vehicle as the wheel movesfrom a depression to a bump at a high rate of speed. The decrease inrate toward the end of the travel is designed to maximize VWT with theuse of a shock absorber that has an increasing spring rate in this area.The increase in spring rate can be made possible by the use of polymerbumpers, but can also be controlled through other means in thespring/damper system, as is well known to those skilled in the art.Linkage configurations can be manipulated to provide varying suspensioncharacteristics, and/or dSR/dVWT values with a change of sign. Thisapplication discloses embodiments that are exemplary configurations ofthe swingarm linkage design of bicycles of the present invention.

While the present invention has been shown and described with regard tocertain preferred embodiments, it is to be understood that modificationsin form and detail will no doubt be developed by those skilled in theart upon reviewing this disclosure. It is therefore intended that thefollowing claims cover all such alterations and modifications thatnevertheless include the true spirit and scope of the inventive featuresof the present invention.

We claim:
 1. A bicycle comprising: a. a bicycle frame; b. a rear wheelsuspension system attached to the frame, wherein the rear wheelsuspension system comprises: i. a rear wheel swingarm comprising a chainstay, a seat stay, and a front stay, wherein the seat stay and the chainstay are attached together by the front stay, and further wherein theswingarm is attached to the frame at a single pivot axis; ii. asubstantially horizontal connecting link coupled to the rear wheelswingarm; iii. a vertical swing link; and iv. a shock absorber pivotallycoupled at a first end to the vertical link and pivotally coupled at asecond end to the bicycle frame, wherein the engagement of the shockabsorber controls a motion of a rear wheel (VWT) of the bicycle, whereinthe shock absorber has a length (SL) between the first end and thesecond end, wherein a change in the vertical wheel travel (ΔVWT) of therear wheel is related to a change in the length of the shock absorber(ΔSL) to provide a shock rate (SR) according to the relationship:SR=ΔSL/ΔVWT and wherein the shock rate (SR) changes throughout thevertical wheel travel of the rear wheel, such that the change in theshock rate dSR/dVWT has a change in sign as the rear wheel travelsthrough the vertical wheel travel.
 2. The bicycle of claim 1 wherein theshock absorber is pivotally coupled at the first end to the verticallink and pivotally coupled at the second end to a top tube of thebicycle frame.
 3. The bicycle of claim 1 wherein the shock absorber ispivotally coupled at the first end to the vertical link and pivotallycoupled at the second end to a down tube of the bicycle frame.